Electrolysis cells are useful for sanitizing water and for the generation of powerful biocides solutions from brine. Many types of electrolysis cell exist for these purposes. The basic feature of some of the most efficient cells is two concentrically disposed cylindrical electrodes with an ion permeable membrane separating the space between the two electrodes to define anode and cathode compartments. Typically an electrolyte solution is passed through the compartments separately or successively to generate the biocide and to sweep the accompanying gases that are generated through the system. The membrane permits the diffusion of electrolytes between the anode and cathode but retard the migration of electrolysis products at the anode and cathode from diffusing to each other reverting back to starting material or undesired side products.
Electrolysis cells using cylindrical electrodes and water insoluble ion permeable membrane or diaphragm between the electrodes have been described for more than 100 years as, for example, that described in U.S. Pat. No. 590,826. U.S. Pat. No. 914,856 describes a cell which permits the flow of electrolyte solutions separately through the anode and cathode compartments using concentric cylindrical electrodes with an ion permeable diaphragm. Numerous improvements have been described since that time including the materials used for fabrication and the features on the component anodes, cathodes, and ion permeable membranes or diaphragms. Less effort has been directed to the assembly process for such cells. The mass production, maintainability, and repairability of these cells have suffered from the nature of the features of the assembly that results. As electrolysis cells have become more extensively employed for water purification, the generation of biocidal solutions, and used in continuous medical and agricultural operations, problems associated with fouling become a consideration in selecting a reliable affordable unit. For this reason the need to easily and reliably produce a maintainable and repairable electrolysis cell assembly has become increasingly important.
Early cells were typically had the electrodes and the diaphragms cemented into place. They were subsequently, cemented, welded, or attached mechanically. Diaphragm material is a particulate material within a bag such that construction required a skilled packer, and the sealing of the material into the system made them impractical to perform maintenance. Membranes were introduced to avoid the problems associated with the packing of the diaphragm. Reliably positioning and attaching the membranes within the cell to achieve sealed anode and cathode compartments remains a problem. The use of soft and flexible polymeric ion permeable membranes are difficult to position and even more difficult to reliably seal. The use of ion permeable ceramic membranes avoid the problems associated with the polymeric membranes due to their soft and flexible nature, but introduce other problems of providing a reliable seal as they are fragile and display a propensity to crack when a stress is applied to them.
A superior compression sealable electrolysis cell assembly is described by Naida et al. in EP0922788 (B1) which has features to impart a spiral circulation of the electrolysis solution through the space between concentric cylindrical tubes. A compression seal is desirable as generally the assembly is used under a slight positive pressure and since a gas is generated and any blockage of flow can impose high pressures of the assembly. A portion of the assembly of EP0922788 (B1) is reproduced in FIG. 1, where an cylindrical electrode tube 4 is positioned outside of an ion exchange diaphragm tube 5 which is positioned outside of an inner rode 4 that functions as the counter electrode and is threaded on the outer ends to apply a compressive force on two bushings 1, or end pieces. These bushings 1 have gaskets 3 placed on seats between the tubes 4 and 5 and the bushings 1 and an o-ring 2 positioned to seal the rod to the bushings. The bushings also display channels 7, or ports, externally ending in pipe connections, or fittings, and proceeding to the electrode chambers 8, which are the spaces between the tubes 4 and 5 and the diaphragm tube 5 and the rod 6, tangentially to the inner generatrix of the base of corresponding cylinders at guide elements 9 placed below the exit from the channels to the electrode chambers. These guide elements 9 are to reinforce the flow of the electrolyte in spiral channels that are initiated by the position of the channels and are a ramp at an angle α to the plane of the gasket seat. The exit of the channels 7 and the guide elements 9 are the width of the electrode chambers 8. The assembly has limitations in that the geometry must include a central rod electrode 6 which is threaded to compress the assembly. This limits the composition of the rod to metals or other electrode materials which can be threaded and withstand the act of compression. The use of gaskets 3 to seal the outer electrode 4 and the ion exchange diaphragm tube 5 results in significant fabrication losses as the compressive force is necessarily imposed upon the ion exchange diaphragm tube 5 resulting in breakage of many units during construction.
The channels 7 described in EP0922788 (B1) must be inserted at an angle β to address the electrode chambers 8 situated between the tubes 4 and 5 and the diaphragm tube 5 and the rod 6. These channels 8 are claimed to exhibit a right edge guide oriented at an angle β greater than 0 degrees and smaller than 90 degrees to a the base elements of the cylinders. Smaller angles are preferable to larger angles to produce the spiraling flow as an angle of 90 degrees imparts no spiral at all and a small angle will increase the number of revolutions between entrance and exit. As the guide elements 9 are situated below the entrance channel 7, and can only increase the angle from that defined by the angle of the channels 7 by deflecting the flow to a higher angle. The guide elements 9 can not attract the flow and reduce the angle of the spiral from that imposed by the flow out of the channel 7. However, to inside edge of the outer tube 4 or 5, or more correctly its gasket 3 that it is resting upon and the outside and inside diameters of the electrode chambers 8 restricts the allowable angles to a much smaller window to that claimed. To achieve an angle less than 15 degrees, the diameter of the channel 7 must be impractically small at the entrance of the chambers 8. The figures and description of EP0922788 (B1), which is also shown in FIG. 1, indicate that the diameter of the channels 7 must match the width of the electrode chambers 8 and would be required for good flow. Given these constraints and the claimed constraints imposed upon the relative diameters of the rod and tubes, the angle for the outside electrode chamber can be no smaller than 24.6 degrees and no larger than 46.1 degrees and the angle for the inside electrode chamber can be from 19.7 degrees to 46.6 degrees, and larger if there is a thickness to the gasket. If the two electrode chambers are nearly equal in width, which would be most reasonable to achieve nearly equal flow rate and pressure, the angle of the channel must be approximately 37 degrees. Although larger angles than 46.6 degrees are not useful to achieve a effective spiral flow they could be achieved by a change in the face from which the channels proceed. The most desirable angle are less than 15 degrees, and they can not be achieved by the geometric requirements imposed in EP0922788 (B1). Therefore although EP0922788 (B1) claims angles from 0 to 90 degrees it teaches how to achieve angles of 19.7 to 46.6 degrees and for other considerations requires an angle of about 37 degrees. The most efficient spiral flow in the electrode chambers is achieved by much smaller angles than 19.7 degrees and these angles are not possible as disclosed in EP0922788 (B1).
The design of EP0922788 (B1) requires that the bushings 1 are in the form of a cap and that the inner electrode rod 6 is longer than the diaphragm tube 5 which is longer than the outside electrode tube 4. Both tubes 4 and 5 must be seated firmly on the gasket 3 and bushing 1 this requirement necessitates that stress is applied to the diaphragm tube 5.
To avoid the imposition of the compression placed on the diaphragm tube an end-cap was designed as described by Daily et al. in US20050183949 which is coassigned with this application. This end-cap is designed to permit the introduction of the electrolyte solutions at only 0 degree angle to the base of the cylinders. Although preferable to an angle greater than 20 degrees, it is not an optimal angle to form a regular spiral in the electrode chambers about the inner tube of the chamber. The end-cap is designed as a combination of three sections which are threaded to seal the sections and the electrode tubes are sealed with an epoxy cement rather than a mechanical compression. There is no seal or physical seat for the diaphragm tube. A tight fit between the orifice of one section of the end-cap and the diaphragm tube is required. By this design, an insufficient seal results in leakage between the two electrode chambers. Slippage of the tube can result in an inner electrode chamber that is blocked from the channel by the tube. Too tight of a fit results in breakage when placing the diaphragm tube into the end-cap section or when a torque is applied when one section is screwed onto the other section. In practice this results in as much as twenty percent breakage during fabrication of the assembly.
The goal of achieving a mass producible electrolysis cell that has a low failure rate of production remains. Furthermore, an easily and reliably manufactured, maintained and repairable electrolysis cell remains a need in the industry. Achievement of smaller more efficient angles of flow entry into the channels to optimize the efficiency of the cell is also desirable.